sim arch: Add non blocking read to devconsole driver

arch/sim/src/up_devconsole.c

@@ -43,6 +43,7 @@
 #include <stdbool.h>
 #include <sched.h>
 #include <errno.h>
+#include <fcntl.h>
 
 #include <nuttx/fs/fs.h>
 
@@ -97,12 +98,13 @@ static ssize_t devconsole_read(struct file *filep, char *buffer, size_t len)
        * on the first read.
        */
 
-      ch = simuart_getc();
+      ch = simuart_getc(!(filep->f_oflags & O_NONBLOCK));
       if (ch < 0)
         {
-          set_errno(EIO);
+          /*  errno is set in upper layer according to returned value */
+
           sched_unlock();
-          return ERROR;
+          return ch;
         }
 
       *buffer++ = ch;

arch/sim/src/up_internal.h

@@ -262,7 +262,7 @@ void up_registerblockdevice(void);
 
 void simuart_start(void);
 int  simuart_putc(int ch);
-int  simuart_getc(void);
+int  simuart_getc(bool block);
 bool simuart_checkc(void);
 void simuart_terminate(void);
 

arch/sim/src/up_simuart.c

@@ -42,6 +42,7 @@
 #include <string.h>
 #include <termios.h>
 #include <pthread.h>
+#include <errno.h>
 
 /****************************************************************************
  * Pre-processor Definitions
@@ -268,7 +269,7 @@ int simuart_putc(int ch)
  * Name: simuart_getc
  ****************************************************************************/
 
-int simuart_getc(void)
+int simuart_getc(bool block)
 {
   int index;
   int ch;
@@ -282,6 +283,12 @@ int simuart_getc(void)
     {
       /* Wait for a byte to become available */
 
+      if (!block && (g_uarthead == g_uarttail))
+        {
+          sched_unlock();
+          return -EAGAIN;
+        }
+
       while (g_uarthead == g_uarttail)
         {
           simuart_wait();